I don't know about you, but I've reached the How Many National Grid 100km×100km Grid Squares Have You Been To? stage of lockdown.
Ordnance Survey cartographers divide up the country into large squares to make grid references manageable. Each square measures 100km by 100km, and each has a two-letter code. Within each square, six figure grid references do not repeat.
On this map, lifted from Wikipedia, only squares which include land are labelled.
England, Wales and Scotland are included but not Northern Ireland (which uses a separate Irish grid instead).
Altogether there are 56 lettered squares. They range from HP (on Unst in the Shetland Islands) to TV (on the Sussex coast at Beachy Head).
The grid is aligned to the 2°W line of longitude (which is the vertical red line on this map).
The first letter in each pair is defined by a larger 500km×500km square. Five such squares - H, N, O, S, T - cover the country. Most of Orkney/Shetland is in H, most of Scotland is in N and most of England and Wales are in S and T.
These large squares are the easiest to enumerate. I've been to N, S and T but not to H and O. The only land within O is an acre of foreshore beneath a North Yorkshire cliff, almost all of which is below the high water mark.
Within each large square the 25 smaller squares are labelled alphabetically from top left to bottom right. For example the top row of N starts NA, NB, NC... and the bottom row ends ...NX, NY, NZ. I is not used.
You can view and explore Britain's 100km grid squares here.
To work out which 100km×100km grid squares I've been to I employed the age-old technique of colouring in a map. I shaded the square if I'd ever stood in it. I decided not to include a square if I'd only driven through it or taken a train through it (although in my case this turned out not to make any difference).
It turns out I've been to every grid square in England apart from OV and SV. OV isn't surprising as it's tiny, inaccessible and almost nobody has been there. SV requires a trip to the Scilly Isles and I've never visited.
Apart from OV and SV, the grid square in England with the smallest area is TV. This covers a thin strip of land along the south coast between Seaford and Eastbourne. If you've been to either, or walked the Seven Sisters and Beachy Head, you can tick off TV. Neighbouring SZ is easier to get to because it includes Bournemouth, Southsea and the Isle of Wight.
Another English tough-to-get is NX on the Cumbrian coast, for which you need to have been to Whitehaven or St Bees. But a trip to Dumfries and Galloway in Scotland also works, and I get to claim NX because I've been to the very northern tip of the Isle of Man.
The bulk of Wales lies within the four squares SH, SJ, SN and SO. Swansea deals with SS and Cardiff with ST. The only Welsh grid squares I've never been to are SM and SR which require a trip to the Pembrokeshire coast. SR can only be attained if you venture onto the peninsula which includes St Govan's Head.
Scotland's a tougher challenge. Glasgow ticks off NS and Edinburgh NT, then Inverness is in NH, Aberdeen in NJ and Dundee in NO. I haven't been to those last three, nor to Oban (NM) or to Fort William (NN), hence my large white Highland gap.
Where I have scored, big time, is the Outer Hebrides. A week on Lewis and Harris provided visits to NA, NB, NF and NG, mainly because I was staying near to where the four squares meet. NA is the real rarity, a brief slice of the Atlantic coast reached at the end of a 12 mile drive along a dead-end single track road, indeed it's possible that none of you have ever been.
The other barely-covered Scottish squares are NK (which is essentially just Peterhead), NL (which requires you to have been to the islands of Mingulay or Tiree) and NW (where you have to have travelled past Stranraer to the coast near Portpatrick).
To summarise, I've been to 35 of Britain's 56 lettered grid squares (which is 62½%). That's all the Ts, all but three of the Ss, just over half of the Ns and none of the Hs and Os.
And then I went one step further and tried working out which of the 35 squares I've properly visited.
First off, in purple, are the six grid squares I've actually lived in. I suspect six is quite a high total, although it helps that SP, TL, SU and TQ all meet in a field near Amersham. I've lived in TQ for most of my life, but SP and TA are covered by university, SU by Job 1, TL by Job 2 and TM by Job 3.
In dark green are the 21 grid squares I've slept in overnight, mostly on holiday, mostly for at least a week. As well as the Outer Hebrides, my other residential triumphs include the Northumberland coast (NU), the Isle of Man (SC), Aberystwyth (SN), Skegness (TF), Margate (TR) and Penzance (SW).
In light green are the eight grid squares I've visited but never stayed in. I'm surprised it's so few. I slept very close to NR but Rothesay's not quite in the right part of the Isle of Bute. I thought I'd stayed in NY on a trip to the Lake District but it turns out Coniston is fractionally south. I've come really close to sleeping in SY but Crewkerne, Poole and Swanage don't quite count. And the invisible one I've missed is TV, that tiny south coast sliver, because a night in Eastbourne has never appealed.
This leaves 14 white unvisited grid squares (plus 7 Hs I've chopped off the top), all 21 of which should be targets for the future.
I'll round off with a summary list.
Lived in: TA SP TL TM SU TQ Slept in: NG NS NT NU NZ SC SD SE SH SJ SK TF TG SN SO SS ST TR SW SX SZ Been to: NA NB NF NR NX NY SY TV Never been: HP HT HU HW HX HY HZ NC ND NH NJ NK NL NM NN NO NW OV SM SR SV
And yes, that's the stage of lockdown I'm currently at.